1. Field of the Invention
The present invention relates to a valve unit disposed in a channel for transporting a fluid and adapted to effect opening and closing by vibrations, as well as a fluid control chip incorporating the valve unit.
2. Description of the Conventional Art
There has been remarkable development in the recent nano technology and microscopic processing technology, and it is expected that these technologies will be merged together henceforth and develop into various application technologies.
As one of such merged technologies, attention has come to be focused on a microelectromechanical systems (MEMS) technology or so-called micromachines in which a semiconductor chip and a microactuator are integrated. In this technology, an LSI and an actuator which performs actual work are integrated and are accommodated in a several-square mm chip. In particular, it is expected that a combination of a microfluidic circuit and an LSI circuit will bring about a new merge.
In such a chip, at least a micropump for supplying a fluid to a channel, that channel, a plurality of sensors, a microvalve for opening and closing the channel, and an LSI circuit for driving them are integrated on a substrate serving as a fluidic circuit. The channel generally has a tube diameter on the order of several micro meters to several hundred micro meters, and the micropump and the microvalve are restricted by the size of this tube diameter.
Incidentally, this microvalve has a microstructure quite different from a general valve, and its function cannot be attained unless problems including leakage of the fluid, the reliability of the opening/closing operation, durability, and the like are resolved. In addition, this microvalve cannot be used as an element of the fluidic circuit of the chip unless its control is easy and accurate. Furthermore, since this microvalve is infinitesimally small, extremely high reliability is required, and it is affected by such inertia, vibration, and dimensional error that can be ignored in general valves.
Accordingly, a quick action type valve suitable for use as such a microvalve has been proposed, as disclosed on U.S. Pat. No. 6,279,872.
FIG. 18 is a schematic diagram of a conventional quick action type valve. This quick action type valve is arranged such that a chamber 101 is provided in a housing 100, and a valve seat 104 closed by a valve element 103 is disposed in its interior. The valve seat 104 is supported by an actuator 105 which is capable of expanding and contracting in the axial direction. The actuator 105 expands and contracts in response to an actuation signal. As a result, the valve seat 104 moves away from the valve element 103 at such a high speed that the valve element 103 cannot follow, and the movement of the valve element 103 is delayed by inertia, thereby forming a flow passing through the valve seat 104. This flow pushes back the valve element 103 to its closed position. The fluid is allowed to flow and controlled by the repetition of such operation. In addition, this quick action type valve can be changed over in a short changeover time, and high repetition speed is attained.
As described in the above, large expectations are placed on the chip in which the microfluidic circuit and the LSI circuit are merged, as described above. However, the microvalve which is incorporated in such a chip has a microstructure quite different from a general valve, and its function cannot be attained unless problems including leakage of the fluid, the reliability of the opening/closing operation, durability, and the like are resolved. In addition, there has been the problem that this microvalve cannot be used as an element of the fluidic circuit of the chip unless its control is easy and accurate. Because it is infinitesimally small, extremely high reliability is required, and it is affected by such inertia, vibration, and dimensional error, and the like that can be ignored in general valves.
In addition, the quick action type valve proposed in U.S. Pat. No. 6,279,872 can be changed over in a short changeover time, and high repetition speed can be obtained. However, since the channel is closed by pressing the valve element 103 against inlet/outlet ports of the valve seat 104 such as a metallic disk, problems are experienced in the reliability of the closing operation, pressure tightness at the time of pressure fluctuations, and so on. Moreover, since the opening of the channel is limited to within operating width (several micro meters to several dozen micro meters) of a piezoelectric element, the accuracy and responsiveness of control is difficult to control and is affected significantly by vibrations, dimensional errors, and the like. In addition, this quick action type valve has a narrow dynamic range, so that a maximum flow rate of the fluid flowing across the quick action type valve cannot be made large. At this time, if an attempt is made to cause the fluid to flow at a high rate and continuously, a large pulsating flow occurs.